[19.0][FIX] website_sale_product_minimal_price: Fix price scale rendering, currency and shop crash

[cristina-hidalgo-tecnativa]

Fixes three v19 regressions in the price scale feature:

• Rendering: the VariantMixin._onChangeCombination monkey-patch is orphaned since core now copies it into WebsiteSale.prototype via Object.assign at import time. Switched to patch(WebsiteSale.prototype, {...}), and fixed the form selector/insertion point (the <form> has no action anymore and Terms/shipping/accordion now live inside it too).
• Currency: the price scale used product.currency_id instead of the pricelist's currency, causing a mismatch between the amount and its symbol.
• Crash: /shop raised AttributeError with chained sub-pricelists because request.pricelist (a lazy wrapper in core) doesn't support |=.

@Tecnativa TT64164
@pedrobaeza @pilarvargas-tecnativa

[OCA-git-bot]

Hi @sergio-teruel,
some modules you are maintaining are being modified, check this out!

[pedrobaeza]

Please remove the patch that is in #1273 (or use temporary reference if needed, but not to hard-copy it), and for the rest, please add an explanation of the what and why in the commit message itself.